X-ray differential absorption microanalysis is presented as a technique for trace element analysis of hydrated biological specimens of about 0.1-5 μm thickness. For the study of the light elements (Z≲20), the absorption technique minimizes the radiation dose and, thus, damage to such specimens when compared with X-ray fluorescence. A Scanning Transmission X-ray Microscope (SXTM) is described, which has been used to map the concentration of calcium in bone with better than 300 nm spatial resolution and a sensitivity to 5% calcium by weight. Future plans are briefly discussed that offer the hope of achieving 0.1% trace element sensitivity and 75 nm spatial resolution.